Section 32-5A-173 When Local Authorities May and Shall Alter Maximum Limits.
Local authorities may change speed limits in some situations, but they must use an engineering and traffic investigation, and some changes need approval from the Department of Transportation or county engineer.
(a) Except as provided in subsection (f), whenever local authorities in their respective jurisdictions determine on the basis of an engineering and traffic investigation that the maximum speed permitted under this article is unreasonable under the conditions found to exist upon a highway or part of a highway, the local authority may set a reasonable maximum limit that does any of the following: (1) Decreases the limit at intersections. (2) Increases the limit within an urban district consistent with Section 32-5A-171. (3) Decreases the limit on any street, unpaved road, or highway under the jurisdiction and control of any county commission. (4) Increases the limit on any street, unpaved road, or highway under the jurisdiction and control of any county commission consistent with Section 32-5A-171. (b) Local authorities in their respective jurisdictions shall determine by an engineering and traffic investigation the proper maximum speed for all arterial streets and shall declare a reasonable maximum limit thereon. (c) Any altered limit established according to this section may be effective at all times, or during hours of darkness, or at other times as may be determined when appropriate signs giving notice thereof are erected upon the street or highway. (d) Any alteration of maximum limits on state highways or extensions thereof in a municipality by local authorities shall not be effective until the alteration has been approved by the Department of Transportation. (e)(1) Not more than six alterations authorized pursuant to this section shall be made per mile along a street or highway, except in the case of reduced limits at intersections. (2) The difference between adjacent limits shall not be more than 10 miles per hour. (f) A municipality may not fix the speed at which motor vehicles may be operated on a county-maintained street, as defined in Section 11-49-80, located within the corporate limits of the municipality unless the municipality conducts an engineering and traffic investigation and receives written approval from the county engineer to fix the speed based on the results of that investigation.